Researchers at the University of Michigan, with colleagues from Michigan State University and Karlsruhe Institute of Technology (KIT) in Germany, report that high surface area silicon carbide (SiC) w/wo 13 wt. % hard carbon (SiC/HC, SiC/O), derived from the carbothermal reduction of silica-depleted rice hull ash (SDRHA), can function as Li⁺ battery anodes that are potentially competitive with silicon anodes.

In an open-access paper in the RSC journal Green Chemistry, the team reports that galvanostatic cycling of SiC/HC and SiC/O shows capacity increases eventually to > 950 mAh g^-1 (Li_1.2-1.4SiC) and > 740 mAh g^-1 (Li_1.1SiC), respectively, after 600 cycles.

SEMs show cycled electrodes maintain their integrity, implying almost no volume expansion on lithiation/delithiation, contrasting with > 300 % volume changes in Si anodes on lithiation. Significant void space is needed to compensate for these volume changes in contrast to SiC anodes suggesting nearly competitive capacities. 6Li MAS NMR and XPS show no evidence of Li_xSi, with Li preferring all-C environments supported by computational modeling. Modeling also supports deviation from the 3C phase at high Li contents with minimal volume changes.

—Yu et al.

Rice hull ash (RHA), a byproduct of rice hull combustion for fuel value, consists typically of 80-90 wt. % amorphous SiO₂ intimately mixed with unburned hard carbon (HC) at the nanoscale. RHA is considered an agricultural waste.

The researchers had earlier described a method of directly extracting SiO₂ from RHA to produce silica-depleted RHA (SDRHA) using an environmentally- and economically-friendly approach.

Mercedes-Benz Research & Development North America (MBRDNA) contributed funding to this work.

Resources

• Mengjie Yu, Eleni Temeche, Sylvio Indris, Wei Lai and Richard M Laine (2022) “Silicon Carbide (SiC) Derived from Agricultural Waste Potentially Competitive with Silicon Anodes” Green Chemistry doi: 10.1039/D2GC00645F